The present invention is directed to an improved pyrometallurgical furnace or reactor. In particular, the invention concerns such a furnace or reactor which incorporates a series of interrelated mechanical stirrers.
While not limited thereto, the features of the present invention are particularly suitable for incorporation into electric arc pyrometallurgical furnaces. Electric arc furnaces have been employed in various circumstances, such as melting and refining iron or steel, smelting ores or sulfide concentrates, and high temperature holding furnaces for cleaning slag or melting and refining copper. While there have been various basic electric arc furnace configurations (the most important of which are discussed below), in addition to the absence of mechanical stirrers in each such configuration, it should be noted that the design of the furnace, and in particular the shape of the vessel which holds the molten material, heretofor has been dictated by the placement of the power electrodes.
A very common prior art furnace design is the "in-line furnace" which is often used in smelting operations. A number (e.g., six) of electrodes are positioned along the centerline of a rectangular furnace and project downwardly into the molten material. This type of furnace has been used, for example, for smelting ilmenite ore.
Round furnaces which can be used for melting and refining metals such as scrap iron or copper, operate on three phase electric power and employ three electrodes positioned at the apexes of an isosceles triangle centered about the center of the circular furnace. When melting metals which can absorb the energy, these furnaces may operate at higher power levels than a typical "in-line" furnace.
While "in-line" and round furnaces are most common, other types have been proposed. One example is something of a hybrid between the "in-line" and the "round" furnaces discussed above, and has been used for cleaning certain types of slags in the copper and nickel industries. This furnace is oval in shape and includes two sets of electrodes for receiving both three-phase power and two-phase power. Both the three electrodes of the three-phase system and the two electrodes of the two-phase system are in an "in-line" configuration.
Despite their design differences, these prior art furnaces have in common the dictation of furnace design by the required electrode array geometry and the absence, other than the electrode geometry and the furnace shape, of any effective means for dispersing the power delivered to the molten material to obtain a uniform temperature throughout the molten material. Additionally, the intimate contact between various phases constituting the molten material, required for enhancing various reactions, has been difficult to achieve. These limitations of prior art furnaces have been vexing problems in the industry. Thus, in a typical prior art "in-line" furnace not only does the heat supplied by the electrodes get concentrated, in a horizontal plane, along the centerline of the furnaces, but, since the electrodes typically just touch the surface of the molten material, a substantial vertical temperature gradient is produced in the furnace. For example, it is not uncommon that a temperature gradient of 150.degree. F can develop between the top and bottom of a furnace having a depth of only 3 to 6 feet. (While the prior art electrodes have been mounted to permit height adjustment, at any given position in molten material they deliver power preferentially to a given level in the molten material.) The non-homogeneous temperature is accompanied by a non-homogeneous composition of the material within the vessel, as well. Thus, various high melting components of the molten material can freeze out at or near the boundary of the slag-matte interface. This not only decreases the efficiency of the reactions desired within the molten material, but can reduce the effective volume of the furnace as frozen matter builds up within the vessel.
Mention should also be made of U.S. Pat. No. 3,861,660 entitled "Pyrometallurgical System With Fluid Cooled Stirrer", issued Jan. 21, 1975 and owned by the Assignee of the present invention. While that patent is not directed to an electric arc furnace, the suggestion of the patent as a whole is that the improved stirrer described and claimed therein is suitable for use in a wide variety of pyrometallurgical systems. While that patent mentions the possible use of the stirrer in electric furnaces, there is no suggestion of what form a large furnace employing such a mechanical stirrer would take.
Accordingly, it is an object of the present invention to provide a pyrometallurgical system with improved uniformity of temperature, and homogeniety of composition, in the molten bath.
A further object of the invention is to provide such a furnace which may be operated at high power densities.
A further object of the invention is to provide an electric arc furnace which can achieve uniform temperatures in the molten bath while permitting more flexibility in the selection of electrode placement.
A further object is to provide a pyrometallurgical system capable of enhancing reactions between constituent materials of the molten bath.